Electroluminescent element employing chrome iron plates



Aug. 10, 1965 w. WESTERVELD ETAL 3,200,279

I ELECTROLUMINESCENT ELEMENT EMPLOYING CHROME IRON PLATES Filed Feb. 1, 1961 FIGJ III/Ill 'I/IIII IIIII INVENTOR WILLEM WESTERVELD LOUIS M. NIJLAND BY HENRI H. JANSSEN AGENT United States Patent 3,26%,279 ELECTRQLUMINEdCENT ELEMENT EMPLGYING CHRGME IRON PLATES Willem Westerveld, Louis Marius Nijland, and Henri Hubert llansseus, all of Emmasingel, Eindhoven, Nethcrlands, assiguors to North American Philips Company, Inc, New York, N.Y., a corporation of Delaware Filed Feb. 1, 1963i, Ser. No. 86,435 Claims priority, application Netherlands, Feb. 4, 1960,

248, Claims. (Cl. 313-103) This invention relates to electroluminescent elements comprising a layer of glassenamel in which the electroluminescent material is embedded and which is provided, on one side, with a metallic carrier and, on its other side, with a conductive layer which is permeable to the radiation emitted by the electroluminescent layer upon applying a potential between the carrier and the conductive layer. The term conductive layer is to be understood herein to mean an electrode galvanically led to the exterior and provided with a terminal. The electrolumines cent materials employed may be, for instance, activated Zinc-sulphides and zinc sulphide-selenides.

It is known to use metal plates or" iron, copper or nickelplated or copper-plated iron as substrata for electrolumiescent elements in which the electroluminescent material is embedded in glassenamel. However, disadvantages then involved are the comparatively poor adhesion to iron or copper of glassenamels which are readily fusible and endured by Zinc sulphides, the poor light output of the element and the low breakdown voltage. However, nickelplating and copper-plating of the iron has not been found sufficient to meet these disadvantages. An element according to the invention provides a solution in which the said disadvantages are avoided.

According to the invention, the surface layer of the metal carrier consists of a metal which can give rise to an oxide layer which is coherent in itself and satisfactorily coherent with the metal. Metals having such a property are Zr, Ti, Ta, Al and Cr. The glassenamel with its coefiicient of expansion matched satisfactorily adheres to the surface layer, since during enamelling the metal of the surface layer gives rise to an oxidic transition layer of high mutual coherence which enhances the adhesion of the glass-enamel, whilst the oxide layer, as previously mentioned, also satisfactorily adheres to the metal. The assembly comprising the carrier and its particular metal surface layer, the oxide layer and the enamel layer containing electroluminescent material constitutes a system of good coherence. With other metals the enamel layer and the oxide film are readily liable to loosen. The oxide layer, according to the period of heating and the atmosphere, has a thiclmess of about 4000 Angstrom and has a uniform colour. it is a dense layer protecting the underlying metal against further oxidation. The oxides of the relevent metals are little reactive in contrast to the metals themselves. The metal layer provided does not itself exhibit slags and cavities which would have an unfavourable influence upon the electroluminescent system, whilst the layer sufficiently covers any cavities and slags of the metal carrier. Consequently, extremely high requirements need not be imposed upon the basic layer in this respect. The oxide layer provided may have a high purity so that no other metal ions are present, which may poison the zinc-sulphide systems, whilst other elements causing difiiculty, such as carbon and silicon, cannot come into contact with the enamel layer either. The surface of the carrier shows no errors which may give rise to annealing colours produced upon heating. Consequently, the carrier is free from spots. After enamelling the layer has a comparatively high reflective capacity. The surface layer has a thickness of at least several hundreds of ice Angstrom according to the basic layer and the spontaneous formation of oxide.

Of the above-mentioned metals chromium is preferred, since the said properties are then most pronounced and this material also has good refiexion properties. More particularly the carrier will be formed so that it consists, for the greater part, of a cheap material, the core of the metal carrier then being of iron.

The surface layer is provided on metal carrier which may be provided, if desired, with one or more metal layers in order to improve the adhesion. Such intermediate layers are matched to the ultimate surface layer. With a metal carrier consisting of iron and a surface layer of chromium, use is made of a nickel layer and/ or a copper layer.

Since for given operating voltage, for example the mains voltage, the light output usually decreases upon increasing thickness of the glassenamel layer, this thickness is not chosen greater than necessary and is preferably from 20 to microns. More particularly the glassenamel layer is built up of a partial layer adjacent the metal carrier and containing titanium dioxide pigment and a partial layer remote from the metal carrier and containing the electroluminescent material. With suitably chosen dimensions and concentrations, such a structure affords the advantage that the light output is higher than in a device having a glassenamel layer which is of the same thickness, but contains electroluminescent material only. In addition, there is a smaller possibility of the electroluminescent material being chemically attacked by the metal carrier, whilst the light emitted by the electroluminescent material is reflected by the partial layer containing the titanium-dioxide pigment. In contrast to known analogous layers containing organic binders instead of glassenamel, the resistivity to breakdown in a structure according to the invention has been found to be approximately the same ineither case. Preference is given to a partial layer containing titanium-dioxide pigment which has a thickness of from 5 to 50 microns, its content of titanium-dioxide pigment being from 5% to 20% by volume. Such a thin layer is sufficient, since due to the dense oxide-layer it is difficult for metal ions to penetrate the enamel layer. The partial layer containing electroluminescent material preferably has a thickness of from 15 to 50 microns and has a content of electroluminescent material of from 20% to 50% by volume.

As regards the glassenamel in which the electroluminescent material is embedded, those glassenamels are preferred which chemically attack the surface layer of the carrier to the least possible extent, since otherwise due to diffusion of metal into the glassenamel the light output would decline as a result of the disadvantageous influence of the metal of the surface layer upon the electroluminescent material. Such attack takes place if the enamel contains many alkaline oxides relative to the acid oxides, and hence in the case of alkaline enamels. Consequently, use is preferably made of glass enamels having a low alkalinity. The alkalinity of a glass may be determined, for example, in the following manner. A glass powder (so-called frit) is manufactured by pouring molten enamel into water, whereby it is burst into many pieces. The acidity of the water is then a measure of that of the glassenamel. A glassenamel of low alkalinity has, for example, a composition of 5 mol. percent of Li O 10 mol. percent of Na O 6 mol. percent of CaO 4.5 mol. percent of SrO 14.5 mol. percent of ZnO 3.5 mol. percent of Ti0 3.5 mol. percent of A1 0 3 23.0 mol. percent of SiO 30.0 mol. percent of B In order that the invention may be readily carried into effect, it will now be described in detail, by way of example, with reference to the accompanying drawing, in which:

FIGURES 1 and 2 are diagrammatic cross-sections of electroluminescent elements, in which the mutual thicknesses of the layers are not shown to scale.

FIGURE 1 is a cross-sectional view of an electroluminescent element according to the invention, comprising an iron carrier 1 provided with a chromium layer 2 on which is a chromiumoxide film 3 which has been pro duced before and during enamelling the carrier. The chromiunrplated carrier is covered with a layer 4 of electroluminescent zinc-sulphide embedded in glassenamel, which has been activated, for example, with copper, silver, gold or manganese and co-activated with aluminium or chlorine. On the side remote from the carrier 1, the layer 4 is covered with a conductive transparent layer 5 consisting of tin-oxide, which is covered for protection with a glass layer 6. The carrier 1 is provided with a terminal 7 and the conductive transparent layer 5 with a terminal 8.

FIGURE 2 is also a cross-sectional view of an electroluminescent element according to the invention, comprising an iron carrier 11 provided with a nickel layer 12 and a chromium layer 13 on which is a chromium oxide film 14 which has been produced before and during enamelling the carrier. The carrier is covered with a glass-enamel layer 15 which is built up of two partial layers, that is to say a partial layer 16 adjacent the carrier and containing titanium-oxide pigment and a partial layer 17 adjacent the carrier and containing electroluminescent zinc-sulphide. The layer 15 is covered with a conductive transparent layer 18 of conducting tin-oxide. The carrier 11 is provided with a terminal 19 and the conductive transparent layer 18 with a terminal 20.

In a particular structure of an element as shown in FIGURE 2, the chromium-plated iron carrier has a thickness of 0.3 mm., the nickel layer provided by electrodeposition has a thickness of about 2 microns and the chromium layer provided by electro-deposition has a thickness of about 1 micron. The partial layer 16 has a thickness of 45 microns and a content of titanium-dioxide pigment of 10% by volume. The partial layer 17, which contains 35% by volume of activated zinc-sulphide, has a thickness of microns. The chromeoxide film 14 has a thickness of 0.2 micron.

What is claimed is:

1. An electroluminescent element comprising a layer of glass-enamel in which the electroluminescent material is embedded and which is provided, on one side, with a metal carrier and, on its other side, with a conductive layer which is permeable to the radiation emitted by the electroluminescent layer upon applying a potential between the carrier and the conductive layer, characterized in that the surface layer of the metal carrier consists of a metal which can give rise to an oxide layer which is coherent in itself and satisfactorily adherent to the metal, said metal being selected from the group consisting of Zr, Ti, Ta, Al and Cr.

2. The electroluminescent element of claim 1, wherein the metal carrier is made of chromium-plated metal.

3. The electroluminescent element of claim 1, wherein the core of the metal carrier consists of iron.

4. The electroluminescent element of claim 3, wherein the metal carrier consists of iron covered with an inter mediate layer of a metal selected from the group consisting of nickel and copper which intermediate layer is covered with a chromium layer.

5. The electroluminescent element of claim 1, wherein the glass-enamel layer has a thickness of from 20 to 80 microns.

6. The electroluminescent element of claim 1, wherein the glass-enamel layer is built up of a partial layer adjacent the metal carrier and containing titanium-dioxide pigment and a partial layer remote from the metal carrier and containing the electroluminescent material.

7. The electroluminescent element of claim 6, wherein the partial layer containing the titanium-dioxide pigment has a thickness of from 5 to 50 microns.

8. The electroluminescent element of claim 7, wherein the content of titanium-dioxide pigment in the relevant partial layer is from 5% to 20% by volume.

9. The electroluminescent element of claim 8, wherein the partial layer containing the electroluminescent material has a thickness of from 15 to 50 microns.

10. The electroluminescent element of claim 9, wherein the content of electroluminescent material in the relevant partial layer is from 20% to 50% by volume.

References Cited by the Examiner UNITED STATES PATENTS 2,866,117 12/58 Walker et al. 2,911,553 11/59 Joorman et al. 2,922,912 1/ Miller.

FOREIGN PATENTS 733,260 7/55 Great Britain.

OTHER REFERENCES Problems in Electroluminescent Television Display, Robert M. Bowie, Sylvania Technologist, XVI, No. 3, July 1958, pages 82 to 85.

Materials Technology for Electron Tubes, by Walter H. Kohl, Reinhold Publishing Corp, 330 W. 42nd St., New York, N.Y., Chapter 4, Glass to Metal Seals.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner. 

1. AN ELECTROLUMINESCENT ELEMENT COMPRISING A LAYER OF GLASS-ENAMEL IN WHICH THE ELECTROLUMINESCENT MATERIAL IS EMBEDDED AND WHICH IS PROVIDED, ON ONE SIDE, WITH A METAL CARRIER AND, ON ITS OTHER SIDE, WITH A CONDUCTIVE LAYER WHICH IS PERMEABLE TO THE RADIATION EMITTED BY THE ELECTROLUMINESCENT LAYER UPON APPLYING A POTENTIAL BETWEEN THE CARRIER AND THE CONDUCTIVE LAYER, CHARACTERIZED IN THAT THE SURFACE LAYER OF THE METAL CARRIER CONSISTS OF A METAL WHICH CAN GIVE RISE TO AN OXIDE LAYER WHICH IS COHERENT IN ITSELF AND SATISFACTORILY ADHERENT TO THE METAL, SAID METAL BEING SELECTED FROM THE GROUP CONSISTING OF ZR, TI, TA, AL AND CR. 